I'm investigating what blockchain technology to use for basically intercompany asset management assets like laptops, shares, intellectual property and other, more complex contracts where party X agrees with Y on Z.

Now, ethereum looks very suitable but I have a few things that I can't seem to find a clear answer to.

1. What if I create a new private blockchain with a genesis file, am I stuck forever with this chain and all its contracts? (i.e. is migrating existing data to another blockchain even possible in any way?)
2. Is the usecase of where X agrees on Y doable? Since contracts cannot read eachothers data. How would you translate existing legal documents to a functional or automated entity? I think that third party, centralized servers would be needed in almost any case where the complexity is slightly more that transfer X value to Y. Because otherwise contracts are meaningless, other than being registered.

example #1:

When time X expires, then invalidate contract Y.

At the very least I would need to externally trigger a new transaction in the blockchain, whenever that time is past?

And in what degree would it be possible to digitalize human-readable contract, albeit simplified versions of it, would one human-contract equate to one solidity contract (or LLL or serpent), or would these have to be cut up, and how would they then communicate with eachother?